Programmably configured switchmode audio amplifier

ABSTRACT

A multi-channel switchmode audio amplifier is configured by a programmed processor such that each channel drives separate loads, is connected in parallel or is configured in a bridge-tied mode as well as combinations thereof. In one embodiment, amplifier channels that are connected in parallel have power amplifiers that are driven with signals from a single modulator. A feedback circuit and error amplifier from one channel controls the modulated signal that is applied to each parallely connected amplifier channel. Current feedback circuits for parallely connected amplifier channels are eliminated by tightly controlling the timing of switching in the power amplifier output stages.

CROSS REFERENCE TO RELATED APPLICATION

This patent application is a continuation of U.S. patent applicationSer. No. 13/777,975, titled Programmably Configured Switchmode AudioAmplifier, filed Feb. 26, 2013, which claims priority to and the benefitof U.S. Provisional Patent Application No. 61/750,744, titledProgrammably Configured Audio Amplifier, filed Jan. 9, 2013, all ofwhich are incorporated herein in their entirety by reference thereto.

TECHNICAL FIELD

The technology disclosed herein relates to switchmode audio amplifiersand in particular to switchmode amplifiers that can drive speakers invarious configurations.

BACKGROUND

Unlike home audio equipment that is generally designed to operate in asingle speaker configuration, commercial audio equipment is oftendesigned to operate in a number of speaker configurations in order todrive speakers with a wide range of impedances. Commercial amplifiers,which can produce between 500-20,000 watts of power, are often designedto be able to drive multiple speakers in parallel or to drive singlespeakers (e.g. subwoofers) to high sound pressure levels. Because it isnot cost effective to design a single amplifier channel that can driveevery different type of load to the same power level, many commercialamplifiers are designed to operate in different modes. These modes caninclude using one channel to drive one or more speakers, combining theoutputs of two or more amplifier channels in parallel to drive one ormore speakers or connecting two or more channels to drive speaker(s) ina bridge-tied load or a combination such as a parallel bridge-tied load.

In order to reduce power loss in amplifiers, many commercial audioamplifiers use switching amplifier topologies such as class D designs.When any amplifier channels are connected in parallel, it is difficultto ensure that each channel contributes equally to current delivered tothe load. To prevent this, multi-channel amplifier designs often employspecial current monitoring feedback circuits that operate to ensure thatthe current delivered by each channel is the same. Such feedbackcircuits not only increase the cost of the amplifier designs but are apotential source of error if each feedback circuit in the amplifier doesnot operate correctly.

Another problem faced by users of commercial audio amplifiers is knowingthe best way to connect their speakers to the amplifier. Many users willwant to drive various combinations of speakers with differentimpedances. The user typically has to review tables or charts that listthe current and voltage capability of an amplifier channel, the loadimpedance of various speakers and speaker configurations and otherfactors in order to determine the best way to drive their speaker loads.The user has to use this information to select a speaker configurationand then determine how to configure the amplifier and connect theirspeakers to the amplifier in the selected configuration.

Given these problems, there is a need for a multi-channel amplifierdesign that is less expensive to manufacture, can handle the currentsharing problem of amplifier stages driving loads in parallel and canaid the user in determining how to best connect their speakers to theamplifier.

SUMMARY

As will be discussed in further detail below, the disclosed technologyrelates to a multi-channel switchmode power amplifier where each channelcan drive separate speaker loads, can be combined with one or more otherchannels to drive loads in parallel or can be configured in abridge-tied load configuration or a combination of such configurations.Each channel includes an error amplifier, a modulator and a poweramplifier stage. A number of signal switches are provided in eachchannel to selectively connect or disconnect an output of a modulator tothe power amplifier stage in the channel. Signal switches are alsoprovided to tie the outputs of the power amplifiers stages together inparallel. When operated in parallel, the signal switches are configuredby one or more programmed processors to connect the output of amodulator from a master channel to the power amplifier stages of one ormore slave channels and to disconnect the modulators in the slavechannels. A single feedback control circuit is used to control theoutput of the modulator for the master channel and no separate feedbackcontrols of the slave channels are needed.

In accordance with another aspect the invention, a programmed processoris configured to receive inputs from a user regarding the number andtype of speaker loads to be driven with the amplifier. The processoraccesses a database that stores specifications for numerous types ofspeakers that can be driven. If the database does not include thespecifications for the particular type of speaker to be driven, theprocessor prompts the user to enter the specification information. Theprocessor then determines a configuration of the amplifier channels thatwill optimally drive the user's speakers. The processor(s) open or closeone or more signal switches in the amplifier to achieve the determinedconfiguration and provides instructions to the user regarding how toconnect their speakers to the amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a programmably configurable, switchmodepower amplifier in accordance with an embodiment of the disclosedtechnology;

FIG. 2 illustrates a number of signal switches in and between amplifierchannels that are selectively opened or closed by a programmed processorin accordance with an embodiment of the disclosed technology;

FIG. 3 illustrates how current sharing between amplifier channels iscontrolled in accordance with an embodiment of the disclosed technology;

FIGS. 4A-4I illustrate a number of different amplifier configurationsthat can be selected by a programmed processor in accordance with anembodiment of the disclosed technology; and

FIGS. 5A-5B illustrate a flow diagram of steps performed by a programmedprocessor to configure an amplifier to drive a desired speaker load inaccordance with an embodiment of the disclosed technology.

DETAILED DESCRIPTION

As will be discussed in further detail below, the technology disclosedherein relates to amplifiers and in particular to switchmode audioamplifiers that can be configured in a number of ways to drive differentspeaker loads.

FIG. 1 is a block diagram of a switchmode multi-channel amplifierconstructed in accordance with an embodiment of the disclosedtechnology. In the embodiment shown, a configurable multi-channelamplifier 50 receives an audio input signal and produces amplified audiosignals on a number different output channels 1-4. The output channels,shown as 1_(out), 2_(out), 3_(out), 4_(out), drive a number of speakerdifferent loads SP₁, SP₂ etc. In one configuration, each output channeldrives a separate speaker load. In another configuration, two or moreoutput channels are coupled together drive a speaker load in parallel.In a third configuration, two or more of the output channels areconnected drive a speaker load in a bridge-tied mode configuration. Ofcourse other combinations are possible such as a parallel bridge-tiedmode where pairs of parallely connected output channels drive a speakerload in a bridge-tied configuration.

A programmed processor 52 such a microprocessor, FPGA, ASIC or othercontrol circuit is configured to receive information from a userselection via an input 54. The input 54 may be a number of keys orbuttons on the amplifier with which the user provides informationregarding the speaker load they would like drive. Alternatively, theinput 54 can be a port configured to receive signals using a directwired or wireless connection or from commercially available wired orwireless networks. A remote control 55 can be a dedicated device similarto a hand-held TV remote control or an application program that operateson a general purpose device such as a smartphone, tablet, computer orother convenient platform. In yet another embodiment, the input 54 is aport and associated communication electronics that are configured toreceive information from a remote computing device (not shown) viacomputer communication link such as the Internet.

As indicated above, the programmed processor 52 is configured to receiveinformation from the user regarding the number and type of speakers theywish to drive. The programmed processor accesses a database 56 thatstores the specifications for a number of common speaker brands ormodels. These specifications include at least the impedance of aparticular brand/model and its maximum power rating. If the databasedoes not include the specifications for the particular brand/model ofspeaker to be driven, the programmed processor produces a prompt on adisplay 58 that asks the user to supply the requested information. Inaddition, the programmed processor 54 receives or prompts the user foran indication of whether multiple speakers are to be driven in parallelor otherwise in a manner that would change the effective impedance ofthe speaker load.

From the information provided, the programmed processor 52 determineshow the amplifier should be configured to drive the desired number andtype of speakers. Some channels may be configured to drive separatespeaker loads. Alternatively, two or more channels may be connecteddrive a speaker load in parallel or two channels may be connected todrive a speaker load in a bridge-tied load configuration or in anothercombination such as parallel bridge-tied load.

In one embodiment, the programmed processor 52 provides a “connectionwizard” that prompts the user with instructions on the display 58 toenter or otherwise provide information regarding the number of speakersthey wish to drive as well as their brand/model and impedance. Theconnection wizard program then determines the appropriate configurationof the amplifier 50 to drive the speakers and sets the position of oneor more switches within the amplifier to configure the amplifier in thedetermined configuration.

In one embodiment, the display 58 is located on the chassis of theamplifier. However the display could also be implemented by sending theinstructions via a wired or wireless communication link to a remotedevice (controller, computer, smart phone etc.).

FIG. 2 is a block diagram of a multi-channel programmable amplifier 50in accordance with an embodiment of the disclosed technology. In theembodiment shown, there are four amplifier channels labeled as channels72, 74, 76 and 78. Although four channels are shown in the disclosedembodiment, it will be appreciated that the programmable amplifier 50could have a greater number (e.g. 8) or a fewer number (e.g. 2) ofchannels if desired. In the embodiment shown, each channel includes thesame major components so only one channel need be described.

Each channel, such as the channel 72, includes an error amplifier 72 a ,a modulator 72 b , a power amplifier stage 72 c and a filter circuit 72d . The error amplifier 72 a has one input that receives an input signalto be amplified and another input that receives a sample of the outputsignal of the amplifier channel via a feedback loop 72 e . The output ofthe error amplifier 72 a is applied to an input of the modulator 72 b .In one embodiment, the modulator 72 b is a pulse width modulator. Theoutput of the modulator 72 b is provided to an input of the poweramplifier stage 72 c . The output of the power amplifier stage 72 c isfed through an inductor/capacitor (LC) filter circuit 72 d that is inturn connected to a speaker terminal (not shown). The feedback loop 72 ecouples a sample of the output of the amplifier channel back to an inputof the error amplifier 72 a to control the signal that is applied to theinput of the modulator 72 b.

In the embodiment shown, a number of signal switches S₁-S₃ selectivelyconnect the inputs of the power amplifiers stages together. A switchS_(i) connects the input of the amplifier stage 72 c to the input ofpower amplifier stage 74 c . A switch S₂ connects the input of the poweramplifier stage 74 c to the input of the power amplifier stage 76 c anda switch S₃ connects the input of the amplifier stage 76 c to the inputof the power amplifier stage 78 c.

As will be appreciated, by closing the switch S₁, the output of themodulator 72 b in channel 72 is supplied to the inputs of both poweramplifier stages 72 c and 74 c . By closing switches S1 and S2, theoutput of the modulator 72 b is supplied to inputs of the poweramplifier stages 72 c , 74 c and 76 c etc.

A number of signal switches S₄-S₆ are provided to selectively connect ordisconnect an output of a modulator in a channel from an input of apower amplifier stage in the same channel. For example switch S₄ isconnected between the output of modulator 74 b and an input of the poweramplifier stage 74 _(c). Switch S₅ is connected between the output ofmodulator 76 b and an input of the power amplifier stage 76 c . SwitchS₆ is connected between the output of modulator 78 b and an input of thepower amplifier stage 78 c.

In the embodiment shown, there is no switch between the output of themodulator 72 b and the input of the power amplifier stage 72 c .Therefore, when operated in parallel, the channel 72 always operates asa master channel (i.e. supplied the signal to drive the power amplifierstages). However, a switch could be provided if desired so that otherchannels could operate as the master channel.

Signal switches O₁-O₃ selectively connect the outputs of the poweramplifier stages together. Specifically switch O₁ connects the output ofpower amplifier stage 72 c to the output of amplifier stage 74 c .Switch O₂ connects the output of power amplifier stage 74 c to theoutput of amplifier stage 76 c . Switch O₃ connects the output of poweramplifier stage 76 c to the output of amplifier stage 78 c.

In one embodiment, the signal switches S₁-S₆ are digitally controlledCMOS switches controlled by the programmed processor. The output signalswitches O₁-O₃ are relays (either mechanical or electronic) withsufficient current carrying capability to handle the currents producedby each power amplifier stage.

As will be appreciated by those skilled in the art, the multi-channelamplifier circuit also includes inverting circuits or programmedsoftware, (which can be done in within a DSP 57) that invert a signalapplied to different channels that drive a speaker load in a bridge-tiedload configuration.

The position of the switches (and whether signal inversion is performed)is controlled based on signals supplied by the programmed processor 52.As indicated above, the connection wizard program determines the mostappropriate amplifier configuration based on the number of speakers tobe driven, their impedance and power handling capability. The programmedprocessor controls the position of the switches in the amplifier andprovides instructions to the user regarding how to connect the speakersto the outputs of the amplifiers.

Depending on the type of speaker load to be driven, any of the channelsin the amplifier can operate as stand alone channels, can be connectedin parallel or can be configured in a bridge-tied load configuration. Ifthe channels are to be connected in parallel, one or more of the outputsignal switches O₁-O₃ between the channels are closed. In addition, theoutput from the modulator of the master channel is connected to theinputs of the power amplifier stages for the slave channel(s). Forexample, if channel 72 is designated as the master channel to beconnected in parallel with the slave channel 74, then the output switchO₁ is closed to connect the outputs of the power amplifier stages 72 c ,74 c together. The switch S₁ is closed to connect the output ofmodulator 72 b to the input of the power amplifier stage 74 c and theswitch S₄ is opened to disconnect the output of the modulator 74 b fromreaching the input of the power amplifier stage 74 c.

Because the switch S₄ is open, the power amplifier stage for the slavechannel is no longer controlled by the feedback loop 74e and the erroramplifier 74 a . In known multi-channel amplifiers, additional feedbackloops are provided to prevent parallely connected amplifier channelsfrom becoming mismatched in the current they provide to the load.However, the disclosed amplifier avoids the need to provide theseadditional feedback circuits by carefully controlling the drivingsignals applied to the power amplifier stages.

FIG. 3 shows a portion of a pair of half bridge amplifier stages thatare connected in parallel. Each stage has a pair of Class-D switchingtransistors 110 a , 110 b , 112 a , 112 b that control how current flowsthrough the stages. When transistor 110 a is closed or conducting,current flows one way through the load and transistor 110 b is open ornon-conducting. The Class-D switches then alternate so that transistor110 b is closed while transistor 110 a is open so that current flows theother way through the load. Each pair of transistors is controlled by agate driver 114 a , 114 b.

If the bridge circuits are connected in parallel and are operatingcorrectly, Class-D switches 110 a and 112 a should open and close atalmost exactly the same time. Similarly, switches 110 b , 112 b shouldopen and close at almost exactly the same time. If however, the timingof the Class-D switches becomes mismatched, then it is possible thatswitch 110 a could be closed at the same time that switch 112 b isclosed. Similarly switch 112 a may be closed at the same time thatswitch 110 b is closed. The result is a short circuit that causes oneamplifier stage to conduct more current than the other stage over theon/off cycle of the half bridge circuit.

One embodiment of the disclosed technology eliminates the need forcurrent feedback circuits in the amplifier by controlling the timing ofthe switches in each power amplifier stage to open or close (conduct orstop conducting) within 100 ns of each other and more preferably towithin 60 ns of each other. Such tight control is achieved by carefullayout and by using fast switching transistors and gate drivers in thepower amplifier stages. In one embodiment, the switching transistors 110a , 110 b , 112 a , 112 b of the half bridges circuits are mosfets,while the gate drivers are configured to have low propagation delay andisolated outputs.

In addition, the traces on the circuit boards of the amplifier arearranged so that any differences in the signal delay from the output ofthe modulator of the master channel to the power amplifier stages of theslave channels are minimized.

Because the timing difference in the switching signals to the switchingtransistors and gate drivers is tightly controlled, any difference inthe current conducted between the parallely connected stages is bufferedby the inductors of the filter sections. Because current cannotinstantaneously change through either inductor, the actual currentsupplied by each half bridge circuit is kept nearly the same without theuse of current control feedback circuitry.

Because the current control loops normally required to equalize thecurrent between the parallely connected power amplifier stages have beeneliminated, the cost to manufacture each switchmode amplifier channel isreduced. In addition, having only a single feedback loop associated withthe master channel to control multiple switchmode amplifier stageseliminates potential sources of circuit instability.

With four channels there are 15 different ways that various speakerloads can be connected. If more channels are present in the switchmodepower amplifier, (e.g. 8 channels) then there are substantially moreconnection configurations that are possible. In one embodiment, theconnection wizard only provides instructions for the most commonly usedspeaker connections. FIGS. 4A-4H show examples of these commonconfigurations for a four channel amplifier embodiment.

In FIG. 4A, the amplifier channel outputs O₁-O₄ drive four separatespeaker loads.

In FIG. 4B, the amplifier channel outputs O₁ and O₂ are connected inparallel to drive a single speaker load, while the channel outputs O₃and O₄ drive separate speaker loads.

In FIG. 4C, the channel outputs O₁ and O₂ connect to a single speakerload in a bridge-tied load configuration, while the channel outputs O₃and O₄ drive separate speaker loads.

In FIG. 4D, the channel outputs O₁ and O₂ are connected in a bridge-tiedload configuration to drive a single load. Channels outputs O₃ and O₄are also connected in a bridge-tied load configuration to drive a singlespeaker load.

In FIG. 4E, the channel outputs O₁ and O₂ are connected in parallel todrive a single load. Channel outputs O₃ and O₄ are also connected inparallel to drive a single speaker load. As used herein “single speakerload” refers to the fact that a single amplifier channel drives one ormore speakers and the single speaker load may itself contain one or morespeakers.

In FIG. 4F, the channel outputs O₁-O₃ are connected in parallel to asingle speaker load, while the channel output O₄ is connected to aseparate speaker load.

In FIG. 4G, channel outputs O₁ and O₂ are connected in parallel to asingle speaker load, while channel outputs O₃ and O₄ are connected in abridge-tied load configuration to drive a single speaker load.

In FIG. 4H, the amplifier is configured such that channel outputs O₁-O₄are all connected in parallel to a single speaker load.

Finally, in FIG. 4I, the channel outputs O₁ and O₂ are connected inparallel, channel outputs O₃ and O₄ are connected in parallel and thepair of parallel channels are connected to a single speaker load in abridge-tied load configuration.

FIGS. 5A-5B show a flow diagram of steps performed by a programmedprocessor to configure an amplifier in order to drive one or morespeakers as requested by the user. As will be understood by thoseskilled in the art, a processor, computer or the like executes a seriesof program instructions stored in a non-transitory computer readablemedia such a flash memory, hard drive, CD ROM or the like. Theinstructions cause the microprocessor to prompt the user for informationabout what type of speakers they want to drive with the amplifier. Afterreceiving the speaker information, the programmed processor configuresthe amplifier in a way that will most appropriately drive the describedload. Although the steps are described in particular order for ease ofexplanation, it will be appreciated that the steps could be performed ina different order or different steps could be performed to achieve thefunctionality described.

Beginning at 200, the programmed processor prompts the user for thenumber and type of speakers to be driven by the amplifier at 202. Theuser can enter the number of speakers to be driven together (e.g. 1-10speakers in parallel), their brand name and model number. At 204, theprocessor looks in a database to determine if the speaker specifications(e.g. impedance and maximum power capacity) are listed in the database.If not, the programmed processor prompts the user to provide thespecification information at 206. At 208, the programmed processorrecalls the speaker specification information. At 210, the programmedprocessor determines if the current required to drive the speaker(s) totheir rated maximum is greater than the maximum current that can beproduced by a single switchmode amplifier channel. If so, the programmedprocessor activates the internal signal switches in the amplifier tocombine two or more amplifier channels in parallel at 212.

At 214, the programmed processor determines if the voltage required todrive the speaker(s) to their maximum power rating exceeds the maximumvoltage that can be produced from a single channel. If so, theprogrammed processor activates sets the position of one or more signalswitches in the amplifier to operate two or more channels in abridge-tied load configuration at 216.

At 218, the programmed processor provides instructions to the user thatindicate how the speakers should be connected to the outputs of theamplifiers. In some cases the speaker load requested by the user mayexceed the capabilities of the amplifier in which case, the programmedprocessor prompts the user to change their desired speakerconfiguration.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

I/we claim:
 1. A multi-channel amplifier, comprising: a number ofamplifier channels for driving speaker loads; a programmed processorthat is configured to: receive input from a user regardingspecifications of a number of speakers to be driven by the amplifier;determine a configuration of the amplifier such that each channel drivesa speaker load, is connected in parallel with another channel to drive aspeaker load or drives a speaker load in a bridge-tied loadconfiguration; and configure one or more channels in the amplifier sothat the amplifier has the determined configuration to drive the desiredspeaker load.
 2. The amplifier of claim 1, wherein the programmedprocessor is configured to provide instructions to the user indicatinghow one or more speakers are to be connected to the multi-channelamplifier.
 3. The amplifier of claim 1, wherein the programmed processoris configured to search a database for speaker specifications based oninput received from a user.
 4. The amplifier of claim 1, wherein thespecifications in the database for each speaker include its impedanceand power rating.
 5. A multi-channel switchmode audio amplifier,comprising: a number of amplifier channels, each including a modulatorand a power amplifier stage having switches and gate drivers; aprogrammed processor that is configured to connect an output of a singlemodulator in an amplifier channel to inputs of two or more poweramplifier stages such that switching differences between the parallelyconnected power amplifier stages is controlled to within 100 nanoseconds.
 6. A multi-channel switchmode audio amplifier, comprising anumber of channels; each including a modulator, a switching poweramplifier stage and a feedback circuit; and a programmed processor thatis configured to connect two more channels in parallel by connecting anoutput of a modulator from a master channel to an input of the poweramplifier stage for one or more parallely connected slave channels; andfor disconnecting the feedback circuit of each slave channel such thatcurrent sharing between the master and slave channels is controlledbased on limiting differences in switching in the power amplifier stagesof the parallely connected master and slave channels to within 100 nanoseconds.